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Old 10-17-2007, 06:35 PM   #1
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Question v8 conversion help, please.

i just wrapped up a v-8 conversion on my 93 lx coupe. When i tried to set my t.p. sensor voltage, i found that it was reading ~3 volts with the key on. I unpluged the sensor and measured the voltage on the signal return on the harness side of the t.p. sensor, it also read ~3 volts. I decided to scan the pcm for codes but my scanner would not scan. The engine harness' is out of a 93 v-8 and my car was a 93 4 cyl. The car runs and drives as long as you keep it under 2000rpm if you go much over that it starts to cut out. All sensors are new and i tried using two different pcm's all with the same effect. Any advice would be great.

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Old 10-18-2007, 07:14 AM   #2
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Re: v8 conversion help, please.

you need to loosen the screws that hold down the TPS a little to get it to move. You want to rotate the TPS after you set initial Idle speed with the Idle screw. . Check your timing ???. Which by the way should be the first thing done before adjusting a TPS. (sometimes you need to use a drill and slightly ovalize the holes for more adjustment )

That is:
1. Check/Set Timing
2. Set Idle screw to desired Idle speed
3. Set TPS idle voltage (by rotating the TPS itself on the TB).

To get a better sense, remove the TP sensor from the throttle body completely. You will see an end sticking out simliar to a flat screwdriver. That will fit into the throttle position sensor. As you push the throttle , it turns. When it turns it changes the voltage that the sensor reports. So if your sensor is set too high, it reports that the throttle is somewhat pressed (to an a small extent but it is still incorrect). When it shows it higher, it tells the computer "Im at this point of the Wide open throttle cycle." Imagine the sensor is reporting equivelant to the pedal being pressed 10% down, but it's actually at 5%. What does it do when it reads higher? It dumps more fuel because you need more fuel to accellerate. Or it could read the other way around. You could be at Wide open throttle (the pedal is being pressed to the floor) but it only reads you are around 3/4 to the floor. You are telling the computer where you are at and it adjusts how much fuel to add (simply put).

When you adjust the idle screw you are opening/closing the throttle butterfly more. Well guess what is sitting on top of the the butterfly? Your TP sensor. So when you adjust the idle screw , you adjust the voltage of the TP sensor because it turns it more one direction that it was already calibrated at. So when you adjust one, you should adjust the other, making sure though the TP sensor is always set last!

Ok. First of all you set the TPS when the car is off and the keys are up (radio comes on). Make sure your voltage meter is DIGITAL , not the sweeping kind. Set it to DC voltage reading, not AC or anything else. Push a sewing needle through the center of the green wire coming off of the TP sensor.You are going to be hooking up the red (positive) wire to the needle that you pushed through. I like to put the black wire (ground) up the the bolt that holds the TP sensor onto the throttle body. Ok by now you know what wire needs to checked and where to hook up your ground. Read your meter. It can read anywhere from 0.00v to 3.00 depending on how messed up it is. As described earlier the meter determines the voltage by how much the butterfly of the throttle body is opened because it rides directly on top. So we must turn the throttle position sensor to match the voltage we need (it is a small fraction of a turn but it still moves some). You are trying to set it at 0.98 volts ! (Anything just under +1.00v is acceptable.)

To turn the throttle position sensor we need to loosen the two bolts that hold it. This allows us to turn the sensor clockwise or counter clockwise. To figure out which way it needs to go you must know where it currently is. If it's too high, you need to lower it. Turn it one direction, if it goes even higher or lower than you need you must turn it the other direction. It can be slightly tedious , turning and checking the voltage. It helps to have a buddy hold the wires on the correct spot and you turn it as necessary so you can read it in realtime. Once you have it set at the right spot tighten the bolts down. Recheck your voltage to make sure it didn't move. If the voltage changed loosen the bolts slightly and try to nudge the sensor so you can still move it but it won't move when you tighten it.


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Old 12-16-2007, 02:29 PM   #3
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Re: v8 conversion help, please.

just a couple ideas...my 92 coupe is a v8 efi conversion, i did by myself, plus i did a v6-to efi v8 '90 t-bird. the last time i had your problem it was ground issue. pins 20-40-60 on your pcm r grounds. try cutting those 3 wires a few inches from the pcm, and ground them straight to the chassis "pcm wires to chassis". i had a similar problem, and that's wut it was...just an idea. when using a factory harness...it is usualy an installation issue if the motor and harness ran fine in another car, but runs like crap in yours......duble check your o2's and make sure you have the heaters hooked up...itsa common overlook on conversions. the heater gets its power from ignition and not through pcm....in lamen terms...on the o2 sensor 2 wires go to pcm, and one goes to an ignition hot, if that makes any sense. when you install the v8 harness ppl forget it cause 2 outa 3 "o2" sensor wires r already in the harness...and they assume that that's all ther is........u may already know this, its just an idea.
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